The invention relates to a granular composite material containing crimped fibers, and to plastic articles made from such material.
In the manufacture and shaping of plastic articles, plastic granules containing additives are often used, whereby these master batch granules are then plastified and mixed intensively with an amount of resin thus forming a viscous mass. This mass can then be shaped into articles by extrusion and/or molding.
In applicant's U.K. Pat. No. 2,150,936, there is described the production of a granular composite containing electrically conductive fibers, e.g., short stainless steel fibers. Such fibers are used for the shaping of thermoplastic articles with antistatic properties or shielding properties against electromagnetic radiation. According to this patent, the content of which is incorporated by reference in the present application, fibers are introduced and uniformly distributed through a plastic by the use of an intermediate granular composite. In addition to conductive fibers, nonconductive fibers, e.g., glass fibers, can also be introduced in the same manner to reinforce the plastic.
Although the dispersion attained according to this patent is good, the injection moulding process conditions must be controlled very accurately. In particular, the shear forces in the warm plastified mass to be injection molded must be controlled to achieve a sufficiently uniform dispersion without excessive fiber breakage. This causes the rate of production to be relatively low.
According to the present invention, a uniform fiber dispersion without significant fiber breakage is achieved under widely varying molding process conditions, such as pressures, temperatures, resin viscosities and throughput, if the fibers in the granular composite are present in an ordered but not too dense packing. This helps to control the gradual release of the fibers by the shear forces occurring during the warm kneading of the granulate and makes this less dependent upon the kind of fiber, its composition, thickness, modulus, etc.